Forget town-hall meetings and letters to the editor. If you want to influence local politics, do what the big boys and girls do: Take out an ad. That's what's happening in the Castro District, where residents and merchants are using poster campaigns to advance policies for dealing with increases in homelessness. Earlier this spring, the first shot--a poster suggesting passersby donate to agencies serving the homeless rather than handing out change--was fired by a coalition of Castro merchants, led by Hot Cookie owner Dan Glazer. In response, an anonymous person (or group) recently produced a cleverly written but poorly reproduced poster calling for the boycott of Hot Cookie and other Castro merchants and labeling the merchants' campaign "un-San Franciscan." Perhaps Mayor Brown should step in and arbitrate (or at least paste up a public policy poster of his own on the issue).